Lithium insertion electrode materials based on orthosilicates derivatives

ABSTRACT

A lithium insertion-type positive electrode material based on an orthosilicate structure and electrical generators and variable optical transmission devices of this material are provided.

This patent application is the National Stage of InternationalApplication No. PCT/EP2007/007288, filed Aug. 17, 2007, which claims thebenefit of priority from U.S. Provisional Application Ser. No.60/839,026, filed Aug. 21, 2006, teachings of which are hereinincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention provides an electrode material of an orderedLi₃PO₄ structure wherein oxygens form a possibly distorted hexagonalclose-packed arrangement and in which all cationic elements are intetrahedral coordination. Electrical generators and variable opticaltransmission devices with at least one electrode comprising thismaterial are also provided.

BACKGROUND OF THE INVENTION

Electrode materials with the olivine structure LiFePO₄ (triphyllite) andthe quasi-isomorphous delithiated material □FePO₄ (wherein □ refers toan Li vacancy; after Li has been removed from LiFePO₄, Fe(2+) shifts toFe(3+) to maintain charge balance) have the advantage of an operatingvoltage of 3.5 V vs. Li⁺/Li°, i.e., in the stability window of bothliquid and polymer electrolytes but with a flat charge/discharge(lithium intercalation) plateau. The favourable properties ofreversibility and appreciably fast kinetics are believed to beassociated with the confinement of both Li and Fe at its two oxidationstates in an octahedral environment. The manganese derivative LiMnPO₄,which is active at 4.2 V vs. Li⁺/Li°, is even more ideally suited towork with liquid electrolytes. For both the Fe and Mn derivatives, theabsence of miscibility at room temperature between the two phases limitsconsiderably the electronic conductivity through small polarons on thetransition metal sites.

DETAILED DESCRIPTION OF THE INVENTION

It has now been found that the confinement of the transition metal ionsand lithium ions to octahedral sites, as in the olivine structure ofLiMPO₄ (M=Fe or Mn or their solid solutions), is not a prerequisite tofavourable electrode properties.

The present invention provides materials for use in electrodes belongingto the ordered Li₃PO₄ structure, as exemplified by Li₂FeSiO₄ andLi₂MnSiO₄ and their solid solutions, in which the oxygens form apossibly distorted hexagonal close-packed arrangement and in which allcationic elements are in tetrahedral coordination. In addition, thestructure of these materials is modified on the anionic or cationicsites or both sites, by aliovalent or isocharge substitutions, toprovide better lithium ion diffusitivity and electronic conductivity.For example, these substitutions allow for the coexistence of iron ormanganese in two different oxidation states in the same phase, orintroduce specific interactions with other elements having redox levelsclose to those of Fe and Mn (e.g., Fe²⁺/Ti⁴⁺

Fe³⁺/Ti³⁺, Mn²⁺/V⁵⁺

Mn³⁺/V⁴⁺, etc.), both of which are favourable to electronicconductivity, while disorder on the anionic site provides preferentialdiffusion sites for Li⁺. Similarly, partial substitution of silicon byphosphorus, vanadium and/or aluminium, allows control of the latticeparameters, and hence the size of the bottlenecks through which thelithium diffusion takes place. In the case of vanadium, extra redoxstates are created increasing the electrode capacity. In addition, andin contrast to LiMPO₄, where the number of electrons per transitionmetal ion is limited to one, with the materials of the present inventionit is possible to exchange more than one electron per transition metalion, especially with manganese and vanadium.

Accordingly, the present invention provides lithium insertion-typepositive electrode materials based on the orthosilicate structure, whosegeneral formula, Formula I, comprisesLi_(x+y)M_(1−(y+d+t+q+r))D_(d)T_(t)Q_(q)R_(r)[SiO₄]_(1−(p+s+v+a+b))[SO₄]_(s)[PO₄]_(p)[VO₄]_(v)[AlO₄]_(a)[BO₄]_(b)

-   -   wherein    -   M is Mn²⁺ or Fe²⁺ or a mixture thereof;    -   D is a metal in the +2 oxidation state selected from the group        consisting of Mg²⁺, Ni²⁺, Co²⁺, Zn²⁺, Cu²⁺, Ti²⁺ and Ca²⁺;    -   T is a metal in the +3 oxidation state selected from the group        consisting of Al³⁺, Ti³⁺, Cr³⁺, Fe³⁺, Mn³⁺, Ga³⁺, Zn²⁺ and V³⁺;    -   Q is a metal in the +4 oxidation state selected from the group        consisting of Ti⁴⁺, Ge⁴⁺, Sn⁴⁺ and V⁴⁺; and    -   R is a metal in the +5 oxidation state selected from the group        consisting of V⁵⁺, Nb⁵⁺ and Ta⁵⁺.        Further, M, D, T, Q, R are all elements residing in the        tetrahedral sites of the Fe ions in Li₂FeSiO₄. The        stoichiometric coefficients for V⁵⁺, Al³⁺ and B³⁺, v, a and b        respectively, each reside in the tetrahedral Si sites of        Li₂FeSiO₄. The stoichiometric coefficients x, y, d, t, q, r, p,        s, v, a, and b are all between zero (inclusive) and one.        Alternatively,        0≦x≦2,        y+d+t+q+r<1,        p+s+v+a+b<1,        and/or        3+2y+a+b=y+t+2q+3r+2s+p+v        where x is the degree of intercalation during operation of the        electrode material.

The present invention also provides an electrical generator comprisingat least one positive electrode and one negative electrode, wherein theat least one positive electrode comprises a material of Formula I andthe at least one negative electrode is a source of lithium ion at a highchemical activity.

Examples of a source of lithium ion for use in the negative electrode ofthe electrical generator of the present invention include, but are notlimited to, metallic lithium, a lithium alloy, a lithium-carbonintercalation compound, a lithium-titanium spinel Li_(4+z)Ti₅O₁₂ (0≦z≦3)and its solid solutions with other spinels, a lithium-transition metalmixed nitride, and any mixtures thereof.

The positive electrode of the electrical generator of the presentinvention may further comprise a conductive additive. An example of aconductive additive for use in the positive electrode of the presentinvention is carbon.

Alternatively, or in addition, the positive electrode may furthercomprise an intercalation material with fast diffusion kinetics.Examples of intercalation materials with fast diffusion kinetics for usein the positive electrodes of the present invention include a lamellardichalcognenide, a vanadium oxide VO_(x) (2.1≦x≦2.5), a Nasicon-relatedmaterial such as Li₃Fe₂(PO4)₃, and a carbon-coated LiFe_(1−α)Mn_(α)PO₄with 0≦α≦1.

In addition, the positive electrode of an electronic generator of thepresent invention may further comprise a polymeric binder. Preferablythe polymeric binder possesses ionic conductivity. Examples of polymericbinders for use in the present invention include, but are not limitedto, a polyester, a methylmethacrylate-based polymer, anacrylonitrile-based polymer, a vinylidene fluoride-based polymer, ahomopolymer or copolymer of tetrafluoroethylene and anethylene-propylene-diene terpolymer. Additional nonlimiting examples ofpolymeric binder include carboxymethyl-cellulose and polystyrenesulfonic acid, both as its hydrogen, lithium, sodium or potassium salt.In one embodiment, the polymeric binder is a polyether, crosslinked ornot, and dissolved in a salt, the cation of which is at least in partLi⁺. In another embodiment, the polymeric binder is swollen by anaprotic solvent and contains a salt, the cation of which is at least inpart Li⁺. Examples of aprotic solvents for use in this embodimentinclude, but are not limited to, ethylene carbonate, propylenecarbonate, dimethylcarbonate, diethylcarbonate, methyl-ethylcarbonate,γ-butyrolactone, a tetraalkylsufamide, a dialkyether of a mono-, di-,tri-, tetra- or higher oligo-ethylene glycols of molecular weight loweror equal to 2000, and mixtures thereof.

Further provided in the present invention is a variable opticaltransmission device comprising transparent semi-conductor coated glassor plastic and two electrodes separated by a solid or gel electrolytes,wherein at least one of the electrodes comprises a material of FormulaI. In one embodiment, this electrode is obtained by laying a thin filmof material of Formula I on a transparent semi-conductor coated glass orplastic by a vacuum deposition technique, sputtering, or from a sol-gelprecursor.

1. A lithium insertion-type positive electrode material based on theorthosilicate structure comprising a compound according to Formula I:Li_(x+y)M_(1−(y+d+t+q+r))D_(d)T_(t)Q_(q)R_(r)[SiO₄]_(1−(p+s+v+a+b))[SO₄]_(s)[PO₄]_(p)[VO₄]_(v)[AlO₄]_(a)[BO₄]_(b)  (I)wherein M is selected from the group consisting of Mn²⁺ and Fe²⁺ andmixtures thereof; D is a metal in the +2 oxidation state selected fromthe group consisting of Mg²⁺, Ni²⁺, Co²⁺, Zn²⁺, Cu²⁺, Ti²⁺ and Ca²⁺; Tis a metal in the +3 oxidation state selected from the group consistingof Al³⁺, Ti³⁺, Cr³⁺, Fe³⁺, Mn³⁺, Ga³⁺, Zn²⁺ and V³⁺; Q is a metal in the+4 oxidation state selected from the group consisting of Ti⁴⁺, Ge⁴⁺,Sn⁴⁺and V⁴⁺; R is a metal in the +5 oxidation state selected from thegroup consisting of V⁵⁺, Nb⁵⁺and Ta⁵⁺; and M, D, T, Q, R are elementsresiding in the tetrahedral sites of the Fe ions in Li₂FeSiO₄; andwherein x, y, d, t, q, r, p, s, v, a, b are between 0 and one; orwherein x is between 0 and 2, y+d+t+q+r are less than 1, p+s+v+a+b areless than 1 and 3+2y+a+b=y+t+2q+3r+2s+p+v.
 2. An electrical generatorcomprising at least one positive electrode and one negative electrodewherein the at least one positive electrode comprises the lithiuminsertion-type positive electrode material of claim 1 and the at leastone negative electrode is a source of lithium ion at a high chemicalactivity.
 3. The electrical generator of claim 2 wherein the at leastone negative electrode comprises metallic lithium, a lithium alloy, alithium-carbon intercalation compound, a lithium-titanium spinelLi_(4+z)Ti₅O₁₂ (0≦z≦3) and its solid solutions with other spinels, alithium-transition metal mixed nitride, or a mixture thereof.
 4. Anelectrical generator of claim 2 wherein the at least one positiveelectrode further comprises a conductive additive.
 5. The electricalgenerator of claim 4 wherein conductive additive comprises carbon. 6.The electrical generator of claim 2 characterized wherein the at leastone positive electrode further comprises an intercalation materialselected from the group consisting of lamellar dichalcognenide, avanadium oxide VO_(x) (2.1≦x≦2.5), a Nasicon-related material and acarbon-coated LiFe_(1−α)Mn_(α)PO₄ with 0<α<1.
 7. The electricalgenerator of claim 6 wherein the Nasicon-related material isLi₃Fe₂(PO₄)₃.
 8. The electrical generator of claim 2 wherein the atleast one positive electrode further comprises a polymeric binder. 9.The electrical generator of claim 8 wherein the polymeric bindercomprises a homopolymer or copolymer of tetrafluoroethylene or anethylene-propylene-diene terpolymer.
 10. The electrical generator ofclaim 8 wherein the polymeric binder possesses ionic conductivity. 11.The electrical generator of claim 6 wherein the at least one positiveelectrode further comprises a polymeric binder.
 12. The electricalgenerator of claim 11 wherein the polymeric binder is a polyethercrosslinked or not and dissolved in a salt, the cation of which is atleast in part Li⁺.
 13. The electrical generator of claim 11 wherein thepolymeric binder is swollen by an aprotic solvent and contains a salt,the cation of which is at least in part Li⁺.
 14. The electricalgenerator of claim 8 wherein the polymeric binder is a polyether, apolyester, a methylmethacrylate-based polymer, an acrylonitrile-basedpolymer, a vinylidene fluoride-based polymer.
 15. The electricalgenerator of claim 11 wherein the polymeric binder iscarboxymethyl-cellulose or polystyrene sulfonic acid, both as itshydrogen, lithium, sodium or potassium salt.
 16. The electricalgenerator of claim 13 wherein the aprotic solvent is ethylene carbonate,propylene carbonate, dimethylcarbonate, diethylcarbonate,methyl-ethylcarbonate, γ-butyrolactone, a tetraalkylsufamide, adialkyether of a mono-, di-, tri-, tetra- or higher oligoethylene glycolof molecular weight lower or equal to 2000, or a mixture thereof.
 17. Avariable optical transmission device comprising transparentsemi-conductor coated glass or plastic and two electrodes separated by asolid or gel electrolytes, wherein at least one of the electrodescomprises the lithium insertion-type positive electrode material ofclaim
 1. 18. The variable optical transmission device of claim 17wherein the electrode comprising the lithium insertion-type positiveelectrode material is obtained by laying a thin film of said material ona transparent semi-conductor coated glass or plastic by a vacuumdeposition technique, sputtering, or from a sol-gel precursor.